This invention relates to a laser beam machining apparatus having a spatial light modulator.
As examples of this kind of laser beam machining apparatus, there are the devices disclosed in Japanese Patent Application Laid-open No. Hei5-77067 (below, xe2x80x9cReference 1xe2x80x9d) and Japanese Patent Application Laid-open No. Sho62-44718 (below, xe2x80x9cReference 2xe2x80x9d). However, with these laser beam machining apparatuses, the light and dark pattern displayed on the liquid crystal spatial light modulator is used simply as an aperture mask. As a result, they have the problem of lowered light utilization efficiency because the majority of the light irradiated from the laser light source is obstructed by the mask and cannot be used in machining.
In contrast, in Japanese Patent Application Laid-open No. Hei6-208088 (below, xe2x80x9cReference 3xe2x80x9d), an optical marking apparatus is disclosed in which readout light is applied to a spatial light modulator and, doing a Fourier transform on the phase-modulated light, an optical image is reconstructed. Because a Fourier transform is used with this optical marking apparatus, theoretically it is possible to use 100% of the readout light for machining. However, because the spatial light modulator has a transmission-type structure, in actuality, light is obstructed by picture element electrodes, wiring, etc., and the light utilization efficiency ends up dropping.
Because transmission-type spatial light modulators, in this way, have the unavoidable disadvantage of decreased light utilization efficiency, thought was given to using a reflection-type spatial light modulator which should be able to avoid this problem. However, by using the reflection-type spatial light modulator as a simple pattern mask, as with the techniques disclosed in above-mentioned Reference 1 and Reference 2, in practice it is not possible to utilize all 100% of the readout light irradiated onto the spatial light modulator.
To deal with this, in Japanese Patent Application Laid-open No. Hei10-186283 (below, xe2x80x9cReference 4xe2x80x9d), a technique is disclosed in which a Fourier transform is performed on the readout light irradiated onto a reflection-type spatial light modulator, and the light utilization factor is improved. In other words, with the technique disclosed in Reference 4, the zero-order light component of the Fourier transform image of the pattern read out from the reflection-type spatial light modulator is phase shifted and, by performing a reverse Fourier transform, it is made to interfere with other light components. By thus forming a re-created image, the contrast ratio of the pattern can be increased.
The inventors, as a result of studying the above-mentioned conventional techniques, discovered the following issue. That is, the technique disclosed in above-mentioned Reference 4 has a structure wherein the re-created image is formed by causing interference between the zero-order light component and other light components. As a result, it only functions effectively in the range of a 25 to 75% duty cycle of the pattern (the portion of the entire screen accounted for by the pattern). In other words, in the technique disclosed in Reference 4, when light of intensity 1 is irradiated from a light source, the intensity I of the output light is given by the following equation:
I(x, y)=2[131 cos(xcfx86(x, y))]
In other words, the intensity I of the outputted light is in the range of 0 to 4, only reaching 4, even at its maximum. Because this equation for intensity I is invariant, theoretically it is difficult to improve the intensity of the output light above this value. Consequently, even if the duty cycle is 25% or below, the intensity of the output light is not improved above this level, but contrast is worsened and light utilization efficiency also decreases.
In this way, the technique disclosed in Reference 4 was unsuitable for machining of patterns where the duty cycle is small, such as the case where for example only one point on the output surface is irradiated, and there was the problem that the level of freedom for machining patterns was restricted.
With the foregoing in view, it is an objective of this invention to provide a laser beam machining apparatus with a high degree of freedom for machining patterns while enabling improvement in the utilization efficiency of the readout light.
The laser beam machining apparatus according to the present invention comprises a reflection-type spatial light modulator, a hologram writing means for writing onto the reflection-type spatial light modulator a hologram pattern corresponding to the desired optical image one wishes to irradiate onto the target, a laser beam irradiation means for irradiating the readout light onto the reflection-type spatial light modulator with incidence angle xcex8, and a Fourier lens for performing a Fourier transform of the readout light which has been phase modulated by the reflection-type spatial light modulator.
With this laser beam machining apparatus, the readout light irradiated onto the reflection-type spatial light modulator is modulated according to the hologram pattern and reflected toward the target. Then the phase modulated readout light is Fourier transformed by the Fourier lens. Whereupon, the desired optical image is imaged and machining is carried out on the specified face of the target irradiated with this optical image. With this laser beam machining apparatus, because the readout light, phase modulated by the hologram pattern in this way, is Fourier transformed so that the desired optical image is imaged, one can achieve improved utilization efficiency of the readout light. In addition, because there are no limits on the duty cycle, there is a high level of freedom for machining patterns.
With the laser beam machining apparatus of this invention, the laser beam irradiation means is provided on an incident light axis inclined by the incidence angle of xcex8 relative to a line normal to the incidence plane irradiated by the readout light of the reflection-type spatial light modulator and the Fourier lens is placed on a reflected beam axis inclined by reflection angle of xcfx86 relative to the normal line within a plane including the normal line and the incident beam axis.
In addition, with the laser beam machining apparatus of this invention, it is preferable if a stage is provided for positioning the target. If this is done, the precision of machining the target is improved.
Further, with the laser beam machining apparatus of this invention, it is preferable if the hologram pattern writing means has storage means for storing the hologram pattern corresponding to the desired optical image to be irradiated onto the target. If this is done, the hologram pattern writing means, simply by reading out the hologram pattern stored in the storage means, can write the hologram pattern onto the reflection-type spatial light modulator. In other words, because the effort of creating a hologram pattern from the desired optical image can be eliminated, it is possible to write the hologram pattern on the reflection-type spatial light modulator at a video rate.
In addition, with the laser beam machining apparatus of this invention, it is preferable for the hologram pattern writing means to have a structure such that a hologram pattern corresponding to a corrected image, that is obtained by modifying the desired optical image by a factor of 1/cosxcex8 in a specified direction, can be written onto the reflection-type spatial light modulator when the desired optical image is irradiated onto said target. If this is done, the readout light irradiated onto the reflection-type spatial light modulator at an incidence angle xcex8 is phase modulated according to the hologram pattern and is reflected toward the target in a state which includes the hologram pattern optical image information. This readout light which includes the hologram pattern optical image information undergoes distortion and is modified by a factor of 1/cosxcex8 in a specified direction. However, because the hologram pattern itself which is the source of the image information included in the readout light corresponds to a hologram pattern of a corrected image modified by a factor of 1/cosxcex8 in the specified direction, relative to the desired optical image, the effect of distortion can be nullified. Then, the readout light with the effect of this distortion removed is Fourier transformed and an image formed. As a result, the desired optical image is irradiated onto the target.
In addition, it is preferable if the laser beam machining apparatus of this invention also has a masking means positioned on the light path of the readout light from the Fourier lens to the target, for cutting zero-order light. By doing this, the readout light irradiated onto the spatial light modulator is modulated according to the hologram pattern. Then, this phase modulated readout light is Fourier transformed by a Fourier lens. Whereupon, the desired optical image and the zero-order light form an image. There, because a masking means is positioned on the light path of the readout light from the Fourier lens to the target, to cut zero-order light, zero-order light is cut by this masking means and only the desired optical image irradiates the target for performing the machining.
In addition, it is preferable that the laser beam machining apparatus of this invention also comprises an imaging lens for imaging the readout light Fourier transformed by a Fourier lens on the specified face of the target and a masking means positioned on the light path of the readout light from the Fourier lens to the imaging lens for cutting zero-order light. By doing this, the readout light irradiated onto the spatial light modulator is phase modulated according to the hologram pattern. Then, this phase modulated readout light is Fourier transformed by a Fourier lens, and the desired optical image and zero-order light together form an image. Then, after zero-order light is cut by the masking means, by means of the imaging lens the desired optical image alone is irradiated onto the specified face of the target and machining is performed.
In addition, it is preferable that the laser beam machining apparatus of this invention also comprises object position recognizing means for acquiring position information on the target, and the hologram pattern writing means has a structure enabling generation of a hologram pattern matched to position of the target, based on position information on the target acquired by the object position recognizing means. If this is done, even if the position of the target, which is the object to be machined, has shifted from the specified position, the hologram pattern writing means can create a hologram pattern matching the target position, based on the target position information acquired through the object position recognizing means. This makes it possible to do precise machining without being affected by variations in target position.
In addition, it is preferable that the laser beam machining apparatus of this invention also comprises physical body shape recognizing means for acquiring 3-dimensional information on the target, and the hologram pattern writing means has a structure enabling generation of a hologram pattern matched to the shape of the target, based on the 3-dimensional information on the target acquired by the physical body shape recognizing means. If this is done, the hologram pattern writing means can create hologram patterns which form 3-dimensional patterns which match the shape of the target based on the 3-dimensional target information acquired by the physical body shape recognizing means. As a result, cases of a distorted pattern being irradiated onto the target become few, and more precise machining can be done.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings. They are given by way of illustration only, and thus should not be considered limitative of the present invention.